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The Unique Type Ib Supernova 2005bf at Nebular Phases: A Possible Birth Event of a Strongly Magnetized Neutron Star

Keiichi MaedaDepartment of Earth Science and Astronomy, Graduate School of Arts and Science, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, JapanMasaomi TanakaDepartment of Astronomy, School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, JapanKen’ichi NomotoDepartment of Astronomy, School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, JapanNozomu TominagaDepartment of Astronomy, School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, JapanKoji S. KawabataHiroshima Astrophysical Science Center, Hiroshima University, Hiroshima, JapanP. A. MazzaliDepartment of Astronomy, School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, JapanHideyuki UmedaDepartment of Astronomy, School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, JapanTakeru K. SuzukiDepartment of Astronomy, School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, JapanTakashi HattoriSubaru Telescope, National Astronomical Observatory of Japan, Hilo, HI 96720

2007en

ABI

Annotatsiya

Late phase nebular spectra and photometry of Type Ib Supernova (SN) 2005bf taken by the Subaru telescope at ~ 270 and ~ 310 days since the explosion are presented. Emission lines ([OI]6300, 6363, [CaII]7291, 7324, [FeII]7155) show the blueshift of ~ 1,500 - 2,000 km s-1. The [OI] doublet shows a doubly-peaked profile. The line luminosities can be interpreted as coming from a blob or jet containing only ~ 0.1 - 0.4 Msun, in which ~ 0.02 - 0.06 Msun is 56Ni synthesized at the explosion. To explain the blueshift, the blob should either be of unipolar moving at the center-of-mass velocity v ~ 2,000 - 5,000 km s-1, or suffer from self-absorption within the ejecta as seen in SN 1990I. In both interpretations, the low-mass blob component dominates the optical output both at the first peak (~ 20 days) and at the late phase (~ 300 days). The low luminosity at the late phase (the absolute R magnitude M_R ~ -10.2 mag at ~ 270 days) sets the upper limit for the mass of 56Ni < ~ 0.08 Msun, which is in contradiction to the value necessary to explain the second, main peak luminosity (M_R ~ -18.3 mag at ~ 40 days). Encountered by this difficulty in the 56Ni heating model, we suggest an alternative scenario in which the heating source is a newly born, strongly magnetized neutron star (a magnetar) with the surface magnetic field Bmag ~ 10^{14-15} gauss and the initial spin period P0 ~ 10 ms. Then, SN 2005bf could be a link between normal SNe Ib/c and an X-Ray Flash associated SN 2006aj, connected in terms of Bmag and/or P0.

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DOI: 10.1086/520054

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